A semiconductor device that operates using an optical signal as an input signal has been known to date. For example, a conventional semiconductor device includes a substrate, a light-receiving device (photodiode), an insulating layer, a light-transmitting conductive layer, and a light-shielding conductive layer. A light-receiving device is formed on the semiconductor substrate. The insulating layer is formed on the semiconductor substrate and covers the light-receiving device. The light-transmitting conductive layer is formed in the insulating layer on the light-receiving device. The light-shielding conductive layer is formed on the insulating layer so that an opening is formed above the light-receiving device.
An optical coupling device (photocoupler) using a combination of a light-receiving device and a light-emitting device of a semiconductor device is also proposed. In the optical coupling device, the light-emitting device converts an input electrical signal to light and emits the light. The light-receiving device receives light from the light-emitting device and converts the light to an electrical signal. In the optical coupling device, upon application of noise (common-mode noise) having a steep riding edge between the light-emitting device and the light-receiving device, a parasitic capacitance between the light-emitting device and the light-receiving device might cause a displacement current. In view of this, proposed is a technique for preventing malfunction by covering the light-receiving device with a light-transmitting conductive layer to shield a displacement current. As the prior-art technique described above, a technique described in Patent Literature 1 is known.